February 2009: Feature Story

All A Bored!
Hopping on the Auger Boring Bandwagon
By Rob Foster

Tunneling through the darkness, diving deeper into the earth, auger boring is the process of simultaneously jacking casing through the earth while removing spoils inside the encasement by means of a rotating flight auger and incorporating the use of a track mounted machine. Auger boring lends itself to many applications, including water, sewer, gas lines, drainage systems, communication cabling and other forms of utilities. In today’s financially conscious world, auger boring is an economical approach when compared with such applications like microtunneling or trenching.

The machine must be savvy in having the technological design and engineered power to tackle the demands of any pressing needs of the job. Aside from superior horsepower, rugged steel-strength construction and state-of-the-art operating control and gauge monitoring systems, auger boring machines have a nomenclature that tells the contractor what it can do. The first number or range of numbers in a machine name, 48/54 for example, means that the master pusher or the cylinder end of the machine is a 48-in. diameter, but can be adapted up to a maximum casing diameter of 54 in. The casing diameter for almost all auger boring machines can be sized down to the smallest casing diameter of 12 in, regardless of the make or model. Today’s manufacturers are also developing machines that can work with larger diameter product — from 84 to 96 in. — which can be installed through the use of like-sized machines. Work for machines of this size has been historically reserved for microtunneling, but current financial constraints are giving auger boring a chance to show its wherewithal in this area.

Safety is always a concern in any working situation, but contemporary machines usually are of a low centerline and wide stance, which prevents rollover during operation.

Adapting to size is important to the machine’s versatility, so the use of adapters both on the master push and at the front end of the track. This permits the casing adapter to be self-aligning, as the inside surface of the strut is tapered to ensure that the product casing centers itself making this a far more efficient product in allowing increased auger boring precision.
The second part of machine nomenclature would be a number such as 900, which is the rating for the maximum pounds of thrust available when multiplied by 1,000. The amount of thrust is important, so that the contractor can match the product size and construction with the length of the bore to ensure that the machine can push the entire amount of product through the bore hole. So in total the machine would be named 48/54-900.

Safety is always a concern in any working situation, but contemporary machines usually are of a low center line and wide stance, which prevents rollover during operation. Some machines also have split machine frames — a feature that allows the unit to be separated into sections to accommodate lighter and faster lifts into and out of the bore pit and aids the operator in being able to facilitate better and safer machine positioning.

Certain manufacturers also have taken the basic concept of auger boring machinery with variations of fast return systems, which can provide up to 10,000 lbs of additional push pull at high speed and create no dogging or winching during retract as the system engages directly to the machine track. This also creates easier machine operation in challenging work climates or conditions.

The bore does not start when the initial bore hole is made, but at site preparation. Knowing the size and makeup of the pit is hypercritical because both play important roles in the outcome of the job. The bore pit size will vary depending on factors involving the size of the product casing, the physical dimension of the machine and the length and width of the machine track. The depth of the pit is determined by the pre-planned engineering for the percent of the grade of the product being installed. The sidewall construction of the pit would consist of either a shored structure, meaning that a concrete or steel fabrication is placed to provide firm skirting to minimize the chance of having a sidewall collapse. The other option is to have a sloped pit, meaning that the dirt is excavated in an angled manner. Either is used depending on the physical ground considerations and infrastructure such as roads or railways that may be within the vicinity of the working area.

The base of the pit should be constructed with rock, concrete or hard pan materials, which provide the machine with a stout working platform, but also serve to level the bore path. If the base is not level, the total production of the bore could be adversely effected, meaning that the line and grade of the product would not be achieved. Many other considerations are made, but these are vital to any auger boring operation.

Besides the machine and site preparation, there are other technologies and equipment that also aid the process. Modern equipment that is relevant to the practice of auger boring includes:

• Water leveling devices that work on the principals of nature are a must-have when maintaining proper auger boring line and grade. Such equipment is designed on the concept that water seeks its own level and uses a sensing head that is welded from the front of the lead product casing and connected to a graduated cylinder. The water level of the cylinder indicates the pitch of the casing. With this knowledge, any driller can make corrections to the grade of the bore.
  
• Bentonite mixing systems deliver the bentonite slurry to the lead casing under pressure to reduce friction. The system also lubricates and supports the pipe while penetrating the soil, assures a better grade, improves thrust capabilities, retards sloughing and cave-ins, extends equipment life and speeds up jacking operation.
• Steering knuckles make possible the ability to make adjustments to the pitch of the steering head and grade of the bore.

Appropriate tooling is also imperative. The use of the always present auger sections should be manufactured with a high-grade plate and mild steel tubing that will rotate and return spoil through the casing back to the auger boring machine and out through the spoil removal door. Most auger sections are also sized to fit inside product casing with at least a 1 1/2-in. wall thickness.

The bore does not start when the initial bore hole is made, but at site preparation. The bore pit size will vary depending on factors involving the size of the product casing, the physical dimension of the machine and the length and width of the machine track.

Ground conditions will determine the type of cutting head that is being employed. For example, more and more auger boring is being done through hard rock, which requires special disc cutter heads that use smooth steel discs to rotate through the rock, cut, return the spoils through the auger section and succeed in formations up to 35,000 psi.

There are also a variety of versatile and field proven cutter designs, which are independently identified for bores through soft rock formations, harp pan, shale, gravel, small boulders and other similar intrusive ground.

Environmental factors are present now more than ever because the world is more sensitive to protecting both human and natural habitats. One critical area to manufacturers is the Tier III- compliant diesel engines requirement, which calls for engines to run cleaner with fewer emissions than prior models. Users should review their own governmental restrictions and contact manufacturers regarding this and other environmental protection practices.

The modern day tried-and-true auger boring method seems to be testing the length of the total bore where the distance may eclipse 500 ft or greater. Such distances are possible and economical, making auger boring a must-have choice when considering a utility or underground technology application.

The total price of the auger boring machine when coupled with the necessary tooling, ancillary equipment and manpower will still be a fraction of the price when compared with the basic six- or seven-figure price tag that just the base model for equipment of the previously described applications would cost a contractor. This is very important when considering that in many areas of the urban United States there are aged utility systems that need to be replaced, especially through new development of retail and commercial properties, requiring every day infrastructure. Auger boring is also becoming a more and more sought after practice in developing or economically established countries that either for the first time are creating infrastructure due to population demands or are facing some of the same critical scenarios as the United States.

None of the above is possible without the realization that auger boring is a complicated process that is coordinated through a careful balance of human patience, knowledge and experience. And that requires the harnessing machine technology, which creates a careful marriage that walks the edge of jobsite success or failure.

Rob Foster is the Marketing Manager for American Augers Inc., based in West Salem, Ohio.